ASME PVHO-1-1997 "Safety Standard for Pressure Vessels For Human Occupancy" focuses on the nonmetallic viewport fabrication and certification. For certification requirements for the pressure hull, you need to look to one of the engineering classing societies such as the American Bureau of Shipping "Rules for Building and Classing Underwater Vehicles, Systems, and Hyperbaric Facilities". If you want to get your pressure hull certified by ABS, you would fall under the guidance given in chapters on Metallic Pressure Boundary Components and Fabrication.